1. Field of the Invention
Exemplary embodiments relate to an array substrate and a method for manufacturing the array substrate. More particularly, exemplary embodiments relate to an array substrate for a liquid crystal display (“LCD”) device and a method for manufacturing the array substrate.
2. Description of the Related Art
Generally, a LCD device includes an array substrate on which switching elements are formed to operate each pixel area, an opposite substrate facing the array substrate and a liquid crystal layer disposed between the array substrate and the opposite substrate. The LCD panel applies a voltage to the liquid crystal layer and controls the transmissivity of light from a backlight assembly, which is typically disposed under the opposite substrate, to display an image.
The array substrate includes a thin-film transistor (“TFT”), which functions as the switching element, and is manufactured using patterns formed in a plurality of photolithographic processes. Generally, a specific mask is used in each photolithographic process, thus numerous masks may be used. However, a four-mask process using four masks has been recently used for manufacturing the array substrate. Because the process uses only four masks, the process is simpler and has lower costs than processes that use a larger number of masks. In the four-mask process, first a metal layer for a data line is etched in a first etching process to form a data line, then the metal layer for the data line and a channel layer formed under the metal layer for the data line are etched in a second etching process to form a source electrode, a drain electrode and a channel portion. The first etching process is a wet etching process and the second etching process includes wet and dry etching processes.
In order to manufacture a large, high resolution LCD device, copper, which has low resistivity, is used for the metal layer for a gate line and/or the metal layer for the data line. In addition, titanium and copper are used at the same time to decrease the resistance of the line.
However, pure titanium easily oxidizes to form a surface oxide layer that is substantially inert to etching gases. Thus a metal layer including titanium is not reactive with and thus not readily etched by an etching gas. Accordingly, the dry etching process may be difficult to perform on a metal layer including titanium.